1. Field of the Invention
The present invention relates to an optical pickup and an optical information apparatus that are suitably applied to an optical disc apparatus for processing different types of optical disc, such as a digital versatile disc-read only memory (DVD-ROM) and a digital versatile disc-recordable (DVD-R).
2. Description of the Related Art
In recent years, the use of optical disc apparatuses has been widespread that record information, such as music content, video content, or a variety of data, on an optical disc serving as a recording medium and play back the information read out of the optical disc.
In practice, the optical disc apparatus emits a write light beam onto concentric tracks or a spiral track formed on a signal recording layer of an optical disc so as to generate a pit having a predetermined shape and record information. In addition, the optical disc apparatus emits a read light beam onto the track and reads out the reflected light beam so as to play back the information.
At that time, the optical disc apparatus detects the partial light beam reflected off the optical disc and carries out predetermined signal processing on the partial light beam. The optical disc apparatus then generates a tracking error signal that varies in accordance with the amount of deviation of the irradiation position from the position of the desired track. Thereafter, the optical disc apparatus carries out tracking control, that is, the optical disc apparatus controls the irradiation position of the light beam on the basis of the tracking error signal to reduce the amount of deviation.
A recordable optical disc, such as a DVD-R or a DVD-RW (digital versatile disk-rewritable) has a groove that serves as a guide groove formed along the track in order to identify the recording position of information on the optical disc. In contrast, a read-only optical disc, such as a DVD-ROM, has no grooves along the track.
Accordingly, the format book of a DVD describes that the tracking error signal is generated using a differential phase detection (DPD) method for a read-only DVD-ROM and is generated using a differential push-pull (DPP) method or a one-beam push-pull (PP) method that uses a push-pull signal for a recordable DVD-R and a DVD-RW.
Additionally, the optical disc apparatuses generate a focus error signal used for accurately focusing the light beam on the signal recording layer of an optical disc on the basis of the partial reflected light beam and generate an RF signal used for reading out information recorded on the optical disc on the basis of the partial reflected light beam.
To perform these methods, an optical disc apparatus is proposed in which a detection area of a photodetector for detecting the light beam reflected off an optical disc is partitioned into a plurality of sub-areas and detection signals detected in the sub-areas are appropriately computed so that a tracking error signal, a focus error signal, and an RF signal that are used for both DPD method and one-beam PP method are generated (refer to, for example, Japanese Unexamined Patent Application Publication No. 2004-281026, in particular, page 71 and FIG. 23, and Japanese Unexamined Patent Application Publication No. 3-5927, in particular, page 9 and FIG. 4).